We have a white powdery looking growth on all buds of our climbing roses. Not on leaves. Only on bases of the buds. We were going to treat for powdery mildew but it isn't on the leaves.
It is still likely Powdery Mildew and given time will likely move down the stems under those buds and then to the leaves. I use a product called Green Cure to spray all of my rosebushes and it works very well on powdery mildew. Here is a link to their website and places to buy it: http://greencure.net/
If you push on the white growth and there is movement or little white bugs come out of it, then the bushes need to be sprayed with an insecticide such as Bayer Advanced Complete Insecticide.